This is weird, but I have seen parents do crazy shit, so I actually wouldn't be shocked this is true.

That said:

How do I convince them I'm not transgender?

Since they don't seem to believe you, at all, you can do several things.

• You could play along, go to the therapist, and then claim you are genderqueer.

• You could lie and say the story was for a friend, who is transgender.

• You could go see the therapist, talk it out, and then convince that person you are not, and never have been, questioning your gender identity.

• You could refuse to take part in this, though I am not sure what your parents will do in retaliation.

Every time I deny it they just take that as further proof that I am.

Your parents seem to put a lot of value on their own opinion of the world. They want to have a special child to show what wonderful parents they are. You are nothing like them, so there has to be a reason you aren't drinking their brand of Kool Aid. "Obviously, our child is just self-hating and scared of who they are. They couldn't agree with our liberal agenda because they are so afraid. Now we can free them." It's BS and stinks of personal gain.

You might want to stop getting upset about it and just state, clearly, "I am not transgender." Only because the more you get upset, and show tears, the more they will take it as self-hatred.

They can't force me into therapy, right? Even if they did, they can't make me take hormones or anything like that? I'm really fucking afraid that they will.

If you are afraid your parents will do something insane like that, then you might want to invent another problem that doesn't involve actual hormones. Maybe you could claim you want to wear make-up and the story was exploring that in a safe way. Buying make-up and then wearing it around the house, but not to school, would likely take their mind off it.

It seems they want to believe you have some horrible thing wrong with you and won't relent.

Personally, I would lie about something less 'shiny' but still equally 'inspiring.' They want to have a child with a new fangled issue.

So just sit them down and tell them, "I am sorry you thought I was transgendered. I am not. I feel like I want to wear make-up and everyone would be creeped out by that. I know you guys are super understanding, so can you give me some money to buy some stuff and I can try it around the house. I am not ready to go public yet, so can we keep this to ourselves and not spread it around."